A boot-band is used both for preventing internal grease and the like from flowing outside a boot and for preventing water or foreign matter from entering inside the boot, by fastening a boot that covers, for example, the power transmission part of an automobile. Because the boot-band is wound around the member to be clamped, the boot-band is usually provided with a pair of boot-band pawls, such that the boot-band can be fastened by applying a fastening tool to the pair of boot-band pawls.
FIGS. 15 and 16 show a first conventional boot-band 1 as described in the specification of Patent Document 1, and FIGS. 17 and 18 show a second conventional boot-band 2 as described in Patent Document 2. Both of the boot-bands 1 and 2 are composed of a band-body 3 that is made of a thin metallic plate and that is wound like a ring. Therefore, when the band body 3 is wound (around the member to be clamped), an outer-layer portion 4 of the band body 3 overlaps an inner-layer portion 5 of the band body 3. The boot and the member that is covered by the boot are placed inside of the ring formed by the boot-band before fastening is done.
In the first conventional boot-band 1, a first boot-band pawl 6 is formed on the outer-layer portion 4, while a second boot-band pawl 7, which to be paired with the first boot-band pawl 6 is formed on the inner-layer portion 5. Engagement holes 8 and 9 are formed in the outer-layer portion 4 in the area between the first boot-band pawl 6 and the longitudinal end (free end) of the outer-layer portion 4. The engagement hole 8 is longer than the engagement hole 9 is, and it is also used as a tack hole for tacking the band body 3. The second boot-band pawl 7, a tack hook 10, and engagement pawls 11, 12 are sequentially arranged on the inner-layer portion 5 in the lengthwise direction of the band body 3 (in the clockwise direction in FIG. 15)
After the boot-band 1 is wound like a ring as shown in FIG. 15, the second boot-band pawl 7 and the tack hook 10 are inserted into the engagement hole 8 of the outer-layer portion 4. Then, by a fastening tool (not illustrated), a pinching force F (see FIG. 16) is applied on the pair of boot-band pawls 6 and 7 in such a manner that the distance between the boot-band pawls 6 and 7 is reduced, which in turn simultaneously reduces the circumference of the boot band and the diameter of the ring formed by the band body. The force F pushes the boot-band pawl 6 into the boot-band pawl 7, simultaneously causing the engagement pawls 11 and 12 to be inserted into, and to be engaged with, the engagement holes 8 and 9, respectively, thus completing the fastening of the boot-band, while firmly maintaining the reduced diameter of the band body.
At this time, because the end section (i.e., the section near the engagement hole 9) of the outer-layer portion 4 tends to be pushed outwardly by the protruding engagement pawl 11, the end section must be pressed radially inward by the force shown as G in FIG. 16, in order to engage the engagement pawl 12 with the engagement hole 9 during the final stage of fastening.
As shown in FIGS. 17 and 18, in the second conventional boot-band 2, a first boot-band pawl 21 is formed on the top of the outer-layer portion 4 and at a location nearest to the longitudinally outer end of the outer-layer portion 4, and a second boot-band pawl 22 that is to be paired with the first boot-band pawl 21 is formed correspondingly on the inner-layer portion 5. Engagement holes 23, 24, and 25 are sequentially formed in the outer-layer portion 4 following the first boot-band pawl 21, and a second boot-band pawl 22, as well as engagement pawls 26, 27, and 28, respectively corresponding to the engagement holes 23, 24, and 25, are sequentially formed on the inner-layer portion 5.
The second boot-band pawl 22 is press-molded in such a manner as to protrude radially outward from the inner-layer portion 5, so that the second boot-band pawl 22 has an opening 22a to receive the first boot-band pawl 21. Also, the first boot-band pawl 21 in the outer-layer portion 4 has a pawl extension 29, which is to be inserted into the opening 22a of the second boot-band pawl 22.
As shown in FIG. 18, when the second conventional boot-band 2 is fastened, a pair of tool pawls 15a, 15b of a fastening tool 15 are applied to the boot-band pawls 21 and 22 by a force shown by F, and then the outer-layer and inner-layer portions 4 and 5 are pushed radially inward, resulting in a reduction of the diameter of the ring-like band body 3. At the time of this pushing in, while the pawl extension 29 is inserted into the opening 22a, the engagement pawls 26, 27, and 28 are engaged with their corresponding engagement holes 23, 24, and 25, respectively, and thus the fastening of the boot-band is completed.    [Patent Document 1] U.S. Pat. No. Re. No. 33744    [Patent Document 2] Japan Patent No. 3001266
In the first conventional boot-band 1, as is shown in FIGS. 15 and 16, a longitudinal force must be applied continuously to the band body 3 by a fastening tool in order to reduce the diameter of the ring, while an inward force must be applied, at the final stage of fastening only, on the outer-layer portion 4 in order to press the outer-layer portion 4 toward the inner-layer portion 5. Therefore, it is required to simultaneously perform two steps—namely, applying both longitudinal and inward forces—which results in a complex fastening process that involves a long operation time and reduced workability.
In contrast, in the second conventional boot-band 2, as is shown in FIGS. 17 and 18, the pawl extension 29 of the first boot-band pawl 21, which is located toward the longitudinally outer end of the outer-layer portion 4, is arranged near to the opening 22a of the second boot-band pawl 22, so that a radially inward-force operation for pressing the outer-layer portion 4 toward the inner-layer portion 5 is not necessary. That is, fastening can be done in one action of pulling in of the boot-band pawls 21 and 22, so that workability is better than that of the first conventional boot-band.
However, in the case of the second conventional boot-band 2, there is a problem that the inner-layer portion 5 might buckle during fastening.
FIG. 19 illustrates the mechanism that causes the buckling 19. A fastening force is applied on the two boot-band pawls 21 and 22, so that the outer-layer portion 4 slides over the inner-layer portion 5 after the pawl extension 29, which is the longitudinally outer end of the outer-layer portion 4, begins to be inserted into the opening 22a. This sliding makes the outer-layer portion 4 climb over the engagement pawls 26, 27, and 28 of the inner-layer portion 5; that is, the outer-layer portion 4 tries to slide with friction against the engagement pawls, the friction force being the greatest at the engagement pawl 26. In the process of such sliding, the outer-layer portion 4 tends to be locked by the friction force at the protruding part of the engagement pawl 26.
As a result of this locking, the force applied to the two boot-band pawls 21 and 22 is in reality applied to the engagement pawl 26 and the boot-band pawl 22, both of which are on the same inner-layer portion 5. As a result, the force for pushing in the outer-layer portion 4 and the inner-layer portion 5—force that should be consumed in the portion of the band body 3 between the two pawls 21 and 22—becomes a force pressing on a small portion of the inner-layer portion 5, between the engagement pawl 26 and the boot-band pawl 22. Then, when the strength of the fastening force exceeds the buckling-resistance limit of that small portion of the inner-layer portion 5, buckling 19 is generated between the engagement pawl 26 and the second boot-band pawl 22 of the inner-layer portion 5. When such buckling 19 occurs, the fastening strength for the member to be clamped becomes unstable and weak, so that the fastening is not secure.